how do they enforce a Compulsory return.?...do they charge you double?thanks

They will come and find you if you don't return as scheduled. You will be dragged from your hiding place and hanged in the Tower of London, or beheaded at Bastille!

Frankly, if a return is cheaper than a one way, throw the second half away. It's not a big deal.

For train travel there is no compulsory return.

Well thank goodness there is no Bastille except they could run me over at the metro stop...
.I couldnt figure out why the leisure fare doesnt say compulsory return....as the other fares do
there are no one way fare IMO...its ridiculous....200-300euro

One-way fares exist as low as $90 in U.S. thru RailEurope - actually it's $90 either one-way or round trip - so the $90 is a tad bit cheaper than the $94 day return, which in fact can often only be booked on the earliest trains on the day, meaning an early reveille. In the U.S. i always recommend contacting BETS (800-441-2387) as they are experts with Eurostars.

Though there seems to be no controls on day returns going only one way it would be easy to do if Eurostar wanted to - they could emulate the ferry boats who would offer day return shopping trips at a fare less than the regular one way fare - they simply would not allow passengers on that had luggage. I've had no reports of Eurostar doing this but it would be easy to implement. But since day returns are only available when Eurostar thinks they will have empty seats i guess it's just a marketing decision to unimpede bogus day returners.

When we bought special fare return tickets we were actually able to buy the segments in different classes. We didn't return in second class!

That's too bad, Marija. It would have been so much nicer to have not returned in first class! LOL